This application is co-pending with my eight other patent applications related to a high pressure air turbine-gear train assembly describing and claiming various aspects thereof.
This invention relates to a high pressure air turbine-gear train assembly and more particularly to a gear tooth alignment technique by accommodation as a means of changing the effective tooth positional accuracy between a first stage gear and a second stage pinion on the same shaft when used with other like units in a parallel or a branched gear system of more than one stage.
When power is transmitted between two stages of any parallel or branched gear system; including epicyclic, star and parallel gear arrangements of more than one stage; any misalignment between the teeth of the first stage gear and the second stage pinion will, when assembled in the gear train, cause unbalanced loading of the gear teeth. The magnitude of the unbalanced load will be a function of the stiffness of the shaft between the gears, the stiffness of the teeth and the extent of the misalignment. First-to-second stage clusters have generally been made as a single member in the past and stringent machining accuracy has been used to result in a reasonable positional accuracy. This can be done when stresses permit machining processes which do not inlcude hardening and grinding, i.e., it is limited to low load applications and/or excessively large gears for high power applications. However, when limited life, lightweight and high loads are dictated, the need for very high wear and bending strength and for optimum load distributions make use of hardened and ground gears mandatory and forces the clusters to be made as two pieces which are then joined to form a compact unit. This joining of two pieces amplifies the positional inaccuracies unless tolerated by some other means. It is thus desirable to have a configuration which provides a means for compensating for the effects of the positional errors after assembly which should also reduce the dynamic increment of load and tooth stresses resulting during operation.